The invention relates to the generation of X-rays and, more particularly, to an improved X-ray source characterized by a relatively small diameter and high power.
X-ray generators are utilized in a variety of applications of practical importance. One significant area in which such sources are employed is the field of X-ray lithography. An illustrative X-ray lithographic system utilized to make structures such as very-large-scale-integrated semiconductor devices is described in an article by M. P. Lepselter entitled "Scaling the Micron Barrier With X-Rays," Technical Digest 1980 IEDM, page 42. An advantageous water-cooled X-ray source for inclusion in such a system is specified by J. R. Maldonado, M. E. Poulsen, T. E. Saunders, F. Vratny and A. Zacharias in "X-Ray Lithography Source Using a Stationary Solid Pd Target," Journal Vacuum Science Technology, Volume 16, page 1942 (1979). Such a source is also described in U.S. Pat. No. 4,258,262.
In an X-ray lithographic system of the proximity printing type, it is well known that the magnitude of a so-called penumbra is deleteriously affected by the fact that the source of X-rays utilized to irradiate a mask in the system is in practice not an ideal point source but has instead a finite size. It is further known that increasing the penumbra decreases the resolution capabilities of the system.
Hence, as the drive towards a submicron (for example, .ltoreq.0.5 micrometers) capability for such an X-ray system continues, various approaches are being explored to decrease the size of the penumbra. One effective way of doing so is to reduce the diameter of the X-ray source included in the system.
Additionally, efforts have been directed by workers at trying to increase the power capabilities of X-ray sources. It was recognized that such efforts, if successful had the potential for decreasing the time required to expose resist-coated wafers in X-ray lithographic systems, thereby increasing the throughput characteristics thereof. Alternatively, in such a higher-power system, the penumbra can be reduced while throughput remains unaffected. This is done by increasing the X-ray source-to-wafer distance while at the same time increasing source power to maintain a constant exposure time.